iStock/Thinkstock(NEW YORK) -- The possibility of a diplomatic solution to the three-year Syrian conflict took another step backward Tuesday after special United Nations-Arab League envoy Lakhdar Brahimi announced he was leaving his post.

Brahimi did not specify his reasons for quitting the job he's held for nearly two years, although U.N. Secretary General Ban Ki-moon speculated it might have had to do with the Security Council failing to arrive at a consensus of how to deal with the civil war that has left more than 150,000 people dead and millions more homeless or relocated.

Russia and China both sit on the Council and have resisted attempts at forcing Syrian President Bashar al-Assad to step down as part of solution to ending the conflict.

Brahimi took over as special envoy to Syria following the resignation in 2012 of former UN Secretary-General Kofi Annan, who expressed similar frustrations with the Security Council.

During his tenure, Brahimi most recently oversaw negotiations in Geneva between members of Assad's government and officials from the Syrian opposition, which went virtually nowhere.

Once describing his job as "nearly impossible," Brahimi said that while a solution to end the bloody war is possible, "the question is how many more dead, how much more destruction there is going to be before Syria becomes again the Syria we have known."